System gets restarted again and again

I am currently using window 7, it was working fine but from past 1 month its getting restarted again and again, One of the technician told us that there is no problem with RAM as he checked it and also with motherboard. Now he is told us that there could be problem with Harddisk. the sytem is one and half year old.

The information on Computing.Net is the opinions of its users. Such
opinions may not be accurate and they are to be used at your own risk.
Computing.Net cannot verify the validity of the statements made on this
site. Computing.Net and Purch hereby disclaim all responsibility
and liability for the content of Computing.Net and its accuracy.